Pressure Wire Helps Identify Severe Aortic Stenosis in Paradoxical Low-Flow/Low-Gradient Cases

WASHINGTON, DC—Invasive hemodynamic assessment may help better identify severe aortic stenosis in patients with low aortic flow/low transvalvular pressure gradients and preserved ejection fractions, new research shows.

Researchers report that classification of severe aortic stenosis using a pressure wire to assess gradient across the aortic valve was concordant with echocardiography in the vast majority of patients with normal-flow/high-grade aortic stenosis, but significantly less so amongst patients with low-flow/low-gradient and normal-flow/low-gradient aortic stenosis.

“In patients who have high-gradient aortic stenosis, which is very well defined, we found that the cath did not offer much,” lead investigator Zaher Fanari, MD (Prairie Heart Institute, Springfield, IL) told TCTMD. “The cath and echo agreed nearly 95% of the time so it’s not an issue. But in [low-flow/low-gradient] aortic stenosis, only 77% of these patients actually had severe aortic stenosis.” 

The results of the study were presented at CRT 2017 in Washington, DC.

Identifying Severe Aortic Stenosis in Paradoxical Patients

Severe aortic stenosis is usually defined by an aortic valve area (AVA) < 1.0 cm2 and a mean transvalvular gradient ≥ 40 mmHg in symptomatic patients. Low-flow aortic stenosis is typically observed in patients with reduced ejection fraction (< 50%) and/or low transvalvular gradient, with the reduced stroke volume resulting from myocardial disease or ventricular dysfunction, among other things.

Patients with reduced flow across the valve and a low transvalvular gradient, despite a preserved ejection fraction, are referred to as paradoxical low-flow/low-gradient aortic stenosis patients. There are no clear echocardiographic criteria which identify those with severe aortic stenosis among those with low-flow/low-gradient aortic stenosis.

One of the reasons it’s important to determine the presence of severe  aortic stenosis in these paradoxical low-flow/low-gradient patients is that they are high-risk and could potentially benefit from TAVR or surgical aortic valve replacement, said Fanari. He added that the American College of Cardiology clinical guidelines previously discouraged the use of invasive assessment of aortic stenosis severity, mainly because of the risk of stroke/transient ischemic attack with crossing the valve, but changed the recommendation from level III to IIb in 2014.

“In the paradoxical low-flow/low-gradient group of patients, they have low flow at the same time they have a normal ejection fraction and it can be tough to confirm they have severe aortic stenosis,” said Fanari. “We don’t really know what to do to diagnose them and the guidelines don’t really give us an answer to confirm they have aortic stenosis.”   

In their study, the researchers identified 297 patients with severe aortic stenosis on echocardiography. Of these, 98 patients had a high transvalvular gradient and 179 had a low gradient. Regarding flow, 159 patients were identified as having reduced stroke volume while 138 had normal flow. In total, there were 117 patients with low-flow/low-gradients and 67 patients with normal-flow/low-gradient.

With invasive catheterization, the researchers crossed the aortic valve retrograde using a fractional-flow reserve (St. Jude Medical) pressure wire to assess the transvalvular pressure gradient and determined cardiac output with thermodilution.

Overall, the use of the pressure wire identified the presence of severe aortic stenosis in 94% of patients with high-gradient aortic stenosis, but in only 77% of individuals with low transvalvular gradients (P=0.02). Invasive testing with the FFR wire identified severe aortic stenosis in 82% of patients with low flow and 83% of patients with normal flow (P=0.89). Of the 117 patients with paradoxical low-flow/low-gradient, severe aortic stenosis was identified in 90 patients. 

Fanari said that patients with normal transvalvular flow and low transvalvular pressure gradients are considered to have moderate aortic stenosis or to be a miscalculation. In these normal-flow/low-gradient patients, however, the use of the pressure wire identified 47 of 67 individuals with severe aortic stenosis. “Many of these patients went on to surgery or TAVR,” said Fanari.

Crossing the valve with the FFR wire was safe, with no strokes or TIAs reported in the cohort.

Discrepancy Between Wire and Echo Findings

To TCTMD, Fanari said the correlation between echocardiography and severe aortic stenosis in patients with high transvalvular gradients is well known, but with low-flow/low-gradient patients the pressure wire can be used to help with disease discrimination, and help to delineate patients who might have only mild or moderate aortic stenosis instead of severe disease.

“I think if you have an aortic valve area less than 1.0 [cm2] on echocardiography, and the patient has a high gradient, then you’ve already proved your point,” said Fanari. “These patients don’t need an extra step. Now, if you have a low ejection fraction and low-flow/low-gradient, you can still do an echo with dobutamine. You still don’t need the pressure wire. I see this being done in patients with an aortic valve area less than 1.0 [cm2], normal ejection fraction, and low-gradient on the echo. These patients should be referred for the wire crossing.”

Speaking with TCTMD, Chris Thompson, MD (St. Paul’s Hospital, Vancouver, BC), said patients with low-flow/low-gradient identified on echocardiography should be classified as indeterminate  until further testing is performed. These patients are typically given dobutamine to alter blood flow to assess the transvalvular gradient with normal flow.

“The best estimate of the severity of aortic stenosis is the projected orifice at normal flow,” he said. If changing blood flow alters the aortic valve area, it isn’t severe aortic stenosis but rather a flow-dependent reduction in the aortic-valve orifice or “pseudo-severe aortic stenosis”.    

For this reason, Thompson challenged the findings, stating the investigators are assuming that the diagnosis of severe aortic stenosis with the pressure wire is correct and echocardiography is wrong. Instead, the results really only show a discrepancy between the echo and pressure-wire classification of severe aortic stenosis. 

“I think the message is that you can do it safely,” said Thompson, referring to use of the FFR pressure wire. “It gives you some more information and is cause for further exploring how decision-making is made in these difficult patients.”

George Michael Deeb, MD (University of Michigan, Ann Arbor), said that low-flow/low-gradient aortic stenosis is frequently encountered in clinical practice, particularly among “little old ladies with a really thick myocardium and a small cavity.” These patients, he told TCTMD, have a small aortic valve area yet a low gradient because the stroke volume is so low.

Joao Cavalcante, MD (University of Pittsburgh Medical Center, PA), said there are a number of additional contributing factors to the low-flow/low-gradient state, such as significant mitral regurgitation, right ventricle dysfunction, tricuspid regurgitation, and pulmonary hypertension, among other factors. “You have to determine if it’s isolated low-flow/low-gradient aortic stenosis or if they have other issues,” added Deeb. As long as the low-flow/low-gradient aortic stenosis is isolated with preserved ejection, these patients do well with surgery or TAVR, said Cavalcante and Deeb.